Classical transplantation-resistance experiments designed to determine whether the R3327 tumor induces specific immunity in syngeneic hosts were performed, but because of technical difficulties, have not yet yielded convincing evidence to suggest that the R3327 tumor is immunogeneic. Further experiments are currently under way to obtain more data. Experiments to test whether non-tumor-antigen-specific immunologic mechanisms might also play a role in transplantation resistance to the R3327 tumor have shown that carrageenan treatment of animals before and after tumor innoculation reduced the capacity of nonimmune host to reject the R3327 tumor. In vitro studies on the mechanism of action of carrageenan suggest that carrageenan treatment reduces natural killer cell activity in splenic lymphocytes; however, these experiments have not yet been performed using R3327 target cells in the assays. Other experiments indicate that carrageenan treatment does not alter serum hemolytic complement titer in the protocol used. We have now established cell lines of both the anaplastic (more than 80 passages) and the hormone-dependent (10 passages) varieties of the R3327 tumor, and plan to use these cell lines as target cells in our future in vitro cytotoxicity assays.